A majority of crown and bridge restorations of teeth continue to be porcelain fused to a metal supporting structure or coping that provides strength for the prosthesis. While “all-ceramic” prostheses are of increasing importance, porcelain fused to metal (PFM) remains cost effective and provides satisfactory aesthetics.
Since the metal substructures used in these restorations are not naturally tooth colored, esthetic veneering porcelains are applied that mimic the color and form of natural teeth. The veneering process plays a critical role in providing a satisfactory restoration. Typically the process of making a PFM restoration requires an opaque layer for masking the metal coping; a dentin layer that simulates the color of the tooth dentin; and an enamel layer that simulates the transparency and neutral colors of the tooth enamel. Other materials such as stains are typically used to achieve aesthetic effects.
Each layer is typically applied by hand, first requiring mixing of selected porcelain powders and liquids. The result is subject to variability and depends upon careful work of a skilled ceramist. Achieving consistent, aesthetic results is time consuming and adds significant cost to the final product, as well as requiring people who have a scarce skill and necessary experience.
In a continuing drive to simplify processes and reduce labor costs, methods have been developed to replace the multi-stage porcelain veneering process by a process in which the veneer material is pressed onto the metal support. However, a remaining difficulty has been that the initial pressing must still often be followed by a hand layering with enamel porcelain, particularly to develop incisal edge translucency.